What is the story of the hydra and Hercules?

Answer 1

Herakles was sent to destroy the Hydra as one of his twelve labours, but for each of her heads that he decapitated, two more sprang forth. So with the help of Iolaos, he applied burning brands to the severed stumps, cauterizing the wounds and preventing regeneration. In the battle he also crushed a giant crab beneath his heel which had come to assist Hydra. The Hydra and the Crab were afterwards placed amongst the stars by Hera as the Constellations Hydra and Cancer.